Manhole frame and cover



Dec. 6, 1966 c. D. RUSSELL 3,289,556

MANHOLE FRAME AND COVER Filed April 14, 1964 INVENTOR C layfon D.Russe!!! Attorney United States Patent 3,289,556 MANHOLE FRAME AND COVERClayton D. Russell, Piedmont, Calif., assignor to Phoenix Iron Works, acorporation of California Filed Apr. 14, 1964, Ser. No. 359,646 1 Claim.(Cl. 941-34) This invention relates to manholes and covers such as thoseused in connection with the distribution of utilities, sewage, drainagesystems, and the like. They are utilized to provide access tounderground vaults and since the latter are often located under roadwaysover which heavy traffic must travel, the construction of the manholeframe and cover must be such that the cover would be easily removablebut at the same time strong enough to withstand highly concentratedloads.

In addition to the foregoing the covers should be able to withstand theexpansion and contraction caused by changes in temperature, but at thesame time the engagement between the frame and cover should be such thatdirt and other foreign matter would not be objectionably lodgedthere-between. A further problem is encountered in the case of loosefitting covers which vibrate and rattle when trafc passes over them. Inaddition to the inherent mechanical weakness under such conditions, thenoise occasioned is very objectionable in residential areas,particularly at night.

Various types of construction have been resorted to in the past toovercome these problems. These have comprised the utilization ofresilient cushions or shims, selflocking slots or lugs between frame andcover, axial serration in the cover, two-part rectangular frame andtriangular cover construction employing three point support, etc. Noneof these have completely solved all the problems enumerated above and inaddition have created problems of their own and in almost every case areexpensive to manufacture and maintain.

It is therefore an object of my invention to provide a manhole frame andcover in which the cover would be many times stronger than those now inuse and still be light enough for easy removal and replacement.

It is another object of my invention to provide a manhole frame andcover which would be reasonably impervious to dirt and water and stillnot be adversely affected by thermal expansion and contraction.

It is still another object of my invention to provide a manhole frameand cover in which the cover would not rattle and create objectionablenoise when subject to surface traffic.

It is finally an object of my invention to provide a manhole frame andcover which would possess all the foregoing advantages and still beeconomical to manufacture and maintain.

I have discovered that by utilizing a cover of solid construction,having my particular conliguration, and adapting it in the manner and inthe dimensional relationship described below, I am able to achieve thedesired results. In particular, and especially with regard to thestrength of the cover, I have discovered that the use of reinforcingribs on the under surface, as is now the case with most existing covers,adds nothing to the strength of the cover.

These covers are customarily made of cast iron which is known to have alow tensile strength and because of their shape and method of support itis diicult to design them using customary methods of engineering stressanalysis. The use of reinforcing ribs would seem to be a logical andnatural expedient, but I have discovered through experimentation thatthis is erroneous and that a solid cover having a curved inner surfaceapproximating that of a sphere, or other solid of revolution, ispreferable, and

in addition to the greater strength it may actually be made lighter inweight, contrary to previous belief.

I have discovered further that when utilizing a cover of my constructionI am able to make the cover thinner and by further adapting it to twithin the frame in the novel manner which I describe below, itsstrength is actually augmented and I am able to obtain a dimensionalrelationship between cover and frame so that I obtain tight or snug litbetween these two, which is highly desirable, without encounteringexpansion and contraction diiculties.

This will become evident to those skilled in the art from thedescription and figures which follow in which:

FIG. l is a top view of the cover of my invention.

FIG. 2 is a cross-section along lines 2--2.

FIG. 3 is a longitudinal section through the manhole frame.

The top surface 1 of the cover is characterized by a diamond shapedtread for skid resistance purposes which is typical of many conventionalmanhole covers. The pick holes 2 are conveniently located through thecover to facilitate removal and replacement. I have discovered that if Ilocate these about 31/2 inches from the outer edge and have their axesinclined at approximately 45, I eliminate the possibility of foreignmatter in the form of long rods from falling into the bottom of thevault. The external inclined peripheral surface of the cover is shown at3, while the lower horizontal machined surface is shown at 5. The bottomsurface of the cover 4 is generally spherical in geometry, although itmay also be a part of a paraboloid or other solid of revolution. When aspherical surface is used I may make the diameter of the sphereapproximately four times the diameter of the cover, which is indicatedat small d. The thickness of the cover at the outer periphery isindicated at T-l, while the thickness at the center is indicated at T-Zon the drawings which will be explained below.

The upper horizontal surface of the frame is machined as is the lowerhorizontal surface 7 to form a ledge as shown. The internal inclinesurface is shown at 8. The inside diameter of the frame at the top ofthe ledge is indicated as D-l, while the outside diameter is indicatedas D-2 and the thickness of the shell at this point is indicated as t.The inside diameter of the manhole opening, or what is known as thenominal diameter of the manhole, is shown as D. The significance of thislettering will also be explained below.

When the cover is in position the cover machined surface 9 will be llushwith machined frame surface 6, while machined surfaces 3 and 5 of thecover will rest snugly against machined surfaces 8 and 7 of the frame.

In order to obtain maximum strength, minimum weight of cover, tightness,and freedom from expansion and contraction problems, I have discoveredthat certain relations must exist between these lettered dimensions.These have een arrived at through prolonged experimentation and verifiedby testing as set out in the charts below. First, considering theexpansion requirements for a given nominal diameter D, there will be acorresponding diameter D-l and D-2 which -deiine the thickness t of theshell at the top of the ledge. For a given temperature rise, t willbecome larger, thereby tending to decrease D-l, but the circumference ofthe frame will tend to get larger also thereby tending to increase D-l.On the other hand, the diameter of the cover d will tend to get largersince the circumference of the cover will also increase. I havediscovered that if I maintain the value of t equal to approximately twopercent of the value of D, these expansions will tend to balance eachother within a wide range of manhole sizes thereby maintaining a snugtit between the cover and frame under all normal conditions. This isimportant not only from the standpoint of tightness but also from thestandpoint of strength, since the snug t tends to stilfen the cover.

I have discovered further that if I make T-l equal to five percent of Dand T-2 approximately equal to seven percent of D, I obtain a conditionof maximum strength of cover utilizing a minimum amount of material. Ihave found also that the optimum angle of inclination of the inclinedsurfaces 3 and 8 to the vertical is elevenand one-half degrees.

Since these dimensions may vary about one-sixteenth of an inch from theideal given above, the dimensions of a typical, standard manhole frameand cover for a twentyfour inch opening would be as follows:

D equals twenty-four inches D-l equals twenty-ve and three-eighthsinches D-2 equals twenty-six and one-quarter inches tequalsseven-sixteenths of an inch d equals twenty-five and ve-sixteenthsinches T-l equals one and one-eighth inches T -2 equals one `andthree-quarters inches Silicon 2.29

Manganese .56 Graphitic carbon 2.86 Combined carbon .63

Phosphorus .336 Sulphur .114 Total carbon 3.49

(The above corresponds to ASTM Spec. A 48-60 T, Class 30) A summary ofthe test results in a typical test series comprising over forty testruns is given below:

Weight of Breaking Sample No. Type of Construction Cover, Load,

Pounds Pounds 200 43, 000 200 44, 515 210 48, 000 170 117, 500 173120,000 plus 177 120,000 plus The plus in the above results indicatesthat this was the capacity of the machine and the cover did not failunder maximum loads produced by the machine.

It is evident from the foregoing that the improvement realized is notjust an improvement in degree but is of the order of magnitude of threeso far as strength is concerned, while the total amount of material usedwith my construction was considerably less in each case.

It will be evident to those skilled in the art that minor changes may bemade in the disclosure above without departing from the method of myinvention and I do not limit myself to the foregoing disclosure, exceptas I do so in the claim which follows.

I claim:

A manhole frame and cover comprising:

a cast iron frame of generally cylindrical configuration;

bearing surfaces machined on the upper circumferen tial edge of saidframe to form an `annular seating ledge therein,

said ledge comprising upper and lower horizontal surfaces and aninternal inclined surface joining said horizontal surfaces and forming apredetermined angle of inclination with the vertical;

a cast iron cover of generally cylindrical configuration;

bearing surfaces machined 0n the outer periphery of said cover,

said bearing surfaces comprising a lower horizontal surface forengagement with said lower horizontal surface of said frame and anexternal inclined surface having a predetermined angle of inclination tothe vertical for engagement with said internal inclined surface of saidframe; pick holes through said cover to facilitate removal of saidcover,

said pick holes being located relatively close to the periphery of saidcover; said pick holes being further characterized by having their axesform an angle of approximately forty-five degrees with the surface ofsaid cover.

References Cited by the Examiner UNITED STATES PATENTS 1,926,595 9/1933Mulvihill 94-35 FOREIGN PATENTS 59,727 2/1954 France. 120,752 6/ 1927Switzerland.

OTHER REFERENCES Neenah Construction Castings, Catalog R 4th Ed.,copyright 1963, page 34 relied on.

CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, Examiner.

N. C. BYERS, Assistant Examiner.

